1. Field of the Invention
The present invention relates to a micropatterned MOS semiconductor device and a process for manufacturing the same.
2. Description of the Related Art
A tendency toward a high-integration and high-speed MOSLSI calls for individual MOSFETs to be miniaturized and micropatterned. In other words, when what is known as the channel length between the source and drain regions in a MOSFET is shortened, the integration of the MOSFET is increased, and the capacity of the gate is decreased, thus allowing high-speed operation of the MOSLSI. On the other hand, when the channel length is shortened, the threshold voltage Vth is decreased due to a short channel effect.
For example, in a MOSFET shown in FIGS. 1A and 1B, as shown in FIG. 1A, When the channel length L is sufficiently larger than the diffusion depth Xj of each of the source and drain regions or the width of the depletion layer, equipotential lines in the channel are substantially parallel to each other, and the operation of the elements does not depend on the channel length L or the diffusion depth Xj, and is kept stable. However, when the channel length L is about 2 .mu.m or less, and is substantially equal to the diffusion depth Xj of the source and drain regions and the width of the depletion layer, the equipotential lines in the depletion layer of the channel region are distorted, as shown in FIG. 1B. The distribution of the equipotential lines depends on the diffusion depth Xj of the source and drain regions and the width of the depletion layer.
For this reason, the threshold voltage Vth of the MOSFET is reduced as the channel length L is decreased, and a very small variation in channel length L causes a large variation in threshold voltage Vth. In addition, punch-throughs between the source and drain regions tend to occur depending on the diffusion depth of the source and drain regions or a drain voltage applied to the drain.
In order to eliminate the above disadvantages, it is important to manufacture a MOSFET having a small diffusion depth Xj. However, the diffusion depth Xj cannot be decreased because of a thermal treatment in the manufacturing process of semiconductor devices.
This poses a big problem when a high integration LSI is manufactured.